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What is “Weather and Chaff” information provided to pilots by ATC?
This one appears in an entry under "Additional Services" in the FAA Pilot/Controller Glossary and claims that ATC provides a wide range of additional services to pilots, including "Weather and Chaff" information, which seems like an unusual entry.  What does "chaff" mean in this context?
Originally chaff was the remains of a wheat plant cut down and with the grains in the head thrashed out, which is then discarded.  It's also a biblical reference to the wicked condemned by God to hell i.e. "the chaff, which the wind driveth away".  In modern times, it is associated with a physical countermeasure to radar whereby thousands of metallic strips are ejected out of an aircraft to confuse enemy radars or break the track of radar guided anti aircraft weapons.  I though the phrase in the P/CG might have been a reference to some sort of anachronistic term about the environment which was termed "chaff" but I don't know.  I did locate this story from NOAA's website where their weather radar in Louisville, KY, was spoofed by military chaff which had been dispersed during nearby training exercises.  This gives though to another risk of an aircraft flying through a cloud of chaff and ingesting it into the engines, or causing some other kind of system damage.  This would seem to be a remote possibility but who knows.  Anybody know what the P/CG meant by chaff in this reference.

Re "It’s also a biblical reference to the wicked condemned by God to hell i.e. “the chaff, which the wind driveth away”." -- well--  we're living in ominous times-- so, might be some need for a NOTAM-- the FAA must consider all eventualities--

When chaff was dropped, ATC was required to give an advisory to aircraft, but it was of a general nature. No special separation criteria, unlike fuel dumping.

Chaff is/was used to distract a radar homing missile, by creating a large target not the aircraft which obscured it. The missile would chase the chaff and run out of propellant without striking the aircraft. Later weapons systems use heat, and as such flares are used as the distraction. Flares are easy to visually recognize day or night, chaff OTOH not so much. If chaff is being dispensed in a MOA for training, you would want know before you transit it at a lower altitude.

When KRCA was a B52 base, it was quite common for those aircraft to drop aluminum chaff (think BIG pieces of tinsel) as part of their training. It would spread out very quickly, and you'd see hundreds of strong primary targets in the area of the drop. They'd hang there for a long time, following the wind. Quite annoying, especially if you had a non-transponder aircraft in the area.
With the B1s that are now based at KRCA, we don't see this anymore, but we occasionally see ECM jamming. It's very effective, but thankfully, it's of short duration.
When these activities are being conducted, we advise all aircraft in the area, so they know that our radar performance may be degraded. It's not the issue that it once was.
Weather services consist of advising pilots of radar displayed weather, but also of forecast weather along the route(AIRMETs), pilot reports (PIREPs - both solicitation AND dissemination), altimeter settings along the route, destination airport weather, and anything else that may assist the pilot with planning the flight.
Once, during a particularly bad day for thunderstorms, I had an American Airlines aircraft, who had just completed multiple weather deviations around BFF, ask about the weather along his route to KEWR. Poor guy was from KSEA, and had to come 200 miles south of his normal route to get around the squall line. I looked at our overhead display, and saw that there was another line of thunderstorms out east, that went from BRD (Brainerd, Minnesota) all the way down to the Gulf.
On the next screen, I saw that the upper winds were from the southwest, 80 knots at FL330, and turned out of the northwest at BRD. I recommended that he go direct BRD, then SLT (Slate Run), which rejoined his flight plan. He called his dispatch. A minute later, he requested the  route I suggested, and informed me that all subsequent aircraft for American going to the east coast would do the same.


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How much mathematics and what level should commercial pilots have?
Continuing off the title, do different types of pilots require different mathematics level? Since as a pilot you have to calculate such as how much fuel will be used and needed, the weight of the cargo, etc. Since all of this will affect your flying since as how very heavy cargo will require more airspeed before taking off.

Meh. You need to know basic math and some algebra. There are charts and tables for nearly all performance questions so the answers are already provided, you just need to know how to use the charts.

So there are potentially two ways to interpret your question. First is a pilot who holds an FAA commercial pilot certification, second is a societal occupation label generally referring to a pilot performing as a crewmember of a 14CFR Part 121 scheduled air carrier airway, or colloquially, an airline pilot.
In both cases the idea that any pilot need to be exceptionally capable at math is a fallacy. I suspect it's a holdover from the 40's and 50's when all flight planning calculations needed to be done by hand. Now all of that is automated and even allowed during the FAA written tests. Additionally, needing strong math skills is often claimed when an individual is actually thinking of a test pilot or aeronautical engineer, which both require very strong algebra and calculus skills.
That said, there are some areas in the higher level written exams that rewrite you know how to calculate weight and balance, but these all relay on standardized some equations that aren't exceptionally difficult for even a novice. These written exams include the Airline Transport Pilot (which will be required for the second interpretation), Dispatcher Certificate, and Flight Engineer.

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text:
Is the Bill Of Sale required for deregistration?
Is the Bill Of Sale required for deregistration?
What are the FAA and EASA regulations applicable?

I really mean de-registration not re-registration. I know that the BOS is required for re-registration but is it required for de-registration.

In the US you don't need a bill of sale because the aircraft may not have been sold. The FAA's definition says:

Deregistered Aircraft An aircraft that has been removed from the U.S. Civil Aircraft Register at the owner's request. Aircraft are
  generally removed for the following reasons: exported, destroyed,
  salvaged, dismantled, or permanently retired from service.

There would be no bill of sale for a destroyed aircraft, for example.
If you're asking about handling the FAA registration when you sell an aircraft, according to AOPA's guide you have to sign and return the current registration certificate, and the FAA will issue a new one to the buyer.

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text:
I want to be an airline pilot. Would becoming a NON-COMBAT Air Force pilot be a good way to become one?
I know that becoming a fighter pilot is highly competitive, making it a difficult route, but would becoming a pilot for an Air Force cargo aircraft or something of the like be a good way to reach my final goal of piloting for an airline?

It's one way but not the only way.

Matters not whether you were flying a fighter or a transport or tanker or even a trainer like the T-6.  The airlines see the hours gained over several years in the Air Force as both highly valuable and highly desirable, regardless of what one has been flying.

It depends on which part of the world you're in.
Airlines based in a country with a healthy General Aviation scene will probably prefer civil pilots. If there General Aviation scene is limited then it would make military pilots an attractive source.
I'm not saying that Military pilots are any worse/better but there have been airlines where the safety record was quite poor as a result of poor CRM from the military pilots, China Airlines and Korean Air are examples. These airlines have recognised and rectified the problems and today are up to industry levels in terms of accidents/incidents.

This isn't true.  Mil pilots are awesome at following procedures and are more of a "known quantity" to airlines.  A fighter pilot, for example, may have fewer hours and less experience in certain areas (like really bad weather, icing, IMC, etc), but that really doesn't matter since most of what they need to know can be trained in relatively easily.  On the other hand, a civil pilot with a varied background and twice the hours may have bad habits that are tougher to train away.  Which pilot is "best?"  Who knows...and it depends on the type of flying being done.

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Are there conventions on which side to travel on Victor airways - USA?
I'm a low-time VFR pilot (100hrs) in the United States. I have not yet started IFR training (other than XC time building).
I understand the purposes and reasons why the Victor airways exist. I also understand the Victor airway widths are 8 NM minimum but widen when the VORs are further than 51 NM apart.
I regularly try to follow the Victor airways and VFR altitudes on VFR Cross Country flights, and do file VFR flight plans and use flight following. This makes it easier for me to communicate my position and seems it would be safer than just flying direct.
Question:
Is there a convention for a side of the "road" you should travel on in the USA?
My guess would be if a convention exists, it would be you should always travel on the right; this puts the red lights of the left wings of crossing traffic together, enforcing / encouraging avoid to the right; both A/C would make turns to the right, further expanding the horizontal gap between them. Right of way to the right, avoid to the right.
Background:
On a recent XC from KIXD to KSGF, I was traveling east at 5500' MSL and was directly over the radial, according to my GPS and my ODI. A west-bound crossing plane on VFR was at 6500' MSL and about 1 NM to the south of the airway. We both were using flight following and were alerted and there were no issues. But it made me pause to think, should I really be centered right on the radial? What if he were as well? Then there would be 0' horizontal separation, only 1000' vertical. And worse, if he were IFR at 6000' and right on the radial, that's even closer.

See Strategic Lateral Offset Procedure (SLOP).

@FredLarson great that's along the lines of what I was looking for.

If you are flying IFR the FAA expects you to be on the centerline of the airway, as per the FAA's IFR flying manual

to operate an aircraft within controlled airspace under IFR, pilots
  must either fly along the centerline when on a Federal airway or...

I can't find any references in the Airplane Flying Handbook to airways at all and keep in mind under VFR "see and avoid" is paramount but centerline is generally accepted. If you are flying with any kind of an autopilot/GPS unit thats where its going to put you.
Moving to your IFR example

And worse, if he were IFR at 6000' and right on the radial, that's
  even closer.

500 is more than enough for the FAA's liking especially when one of those planes is flying under IFR.

Most airways are eight nautical miles (14 kilometers) wide, and the
  airway flight levels keep aircraft separated by at least 500 vertical
  feet from aircraft on the flight level above and below when operating
  under VFR.

The reality is there is often even more separation since under VFR you are required to stay 500 below the cloud bases which are not always at round numbers you may often end up at the next lowest VFR cruising altitude
It is however, advised that if you are flying IFR but climbing on an airway in VFR conditions you execute gentle banks to look for traffic.

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Do I need a driver's license to get a PPL in Canada?
I've been searching on Google but there doesn't seem to be any results confirming or rejecting the requirement of a driver's license prior to PPL. It returns results for the United States, but that is of no use to me.
There is this question, but it doesn't address the having or not having a driver's license prior to PPL.
I have looked at the flight school (a),(b). Unless I am blind, there is no reference to this matter.
It seems like a very obvious question to ask, I'm surprised there is no reference.
If someone could point me to resources, or if someone obtained their PPL prior to driver's license could provide a briefing of whether this is an obvious requirement and I am oblivious to it or is it not a requirement at all.

Welcome to Av.SE.

I'm not aware of any country where a DL is a prerequisite for a PPL, which makes sense since few (if any) of the skills transfer.  However, it's generally hard to prove a negative; there's unlikely to be a law that says you don't need one, just a lack of laws saying you do need one.

@StephenS there are quiet a bit transferable skills, which are required for flight
1. Spatial abilities ( i.e. parallel parking )
2. Short reaction time to events
3. Ability to monitor multiple displays at once
4. Alertness and awareness of surroundings (i.e. not zoning out)
5. Procedural memory
Hence the surprise of why a driver's license is not mentioned

(1) Fair enough, but remember you're moving in three dimensions, rather than one-and-a-half, and not necessarily in the direction the nose is pointed. (2) I'd argue that with a few exceptions, correct response is far more important in aviation than a quick response, as long as there isn't an inordinate delay. (3) You shouldn't really monitor all instruments at once, but you should develop good instrument scan technique. (4) Situational awareness should be drilled into you from day one of primary training by any decent instructor. (5) That's what training and rehearsal is for.

@Mel none of those items you list are taught in driver's ed (in the USA). At least not my recollection of my driver's ed class, nor when my 3 kids went through it.

@Mel: One could argue that pilot training is a much better (and safer) way to acquire the skills you list, rather than driver training. Many years ago I knew a young student pilot whose father was an air force veteran. His father insisted that his son get his pilot license before learning to drive a car, since driving was so much more dangerous. I think he had a point.

It does not appear that a driver's license is required. From General information on pilot licences and permits, which details the requirements for getting various kinds of pilot licenses, there is no mention of a driver's license.

Prior to the issue of a permit or licence, an application must be submitted and the following requirements met:

proof of age and citizenship (not required if previously submitted)
proof of medical fitness;
proof of having met the knowledge requirements;
proof of having met the skill requirement;
proof of having met the experience requirement;
payment of the appropriate fees.

CAR 421.06 lists the documents that are accepted as proof of citizenship and proof of identification when you apply for a Canadian pilot's license. A driver's license isn't listed so I assume it isn't even accepted for those purposes, never mind required.
CAR 401.03 lists the documents that you have to have on you when flying, and there are only two: your license and your medical.
So it appears that a driver's license isn't required to either get or use a PPL.


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Would there be a restriction on my Sport Pilot license if I do my checkride in an aircraft without rudder pedals like the Ercoupe?
I am training in an Ercoupe 415-C (C-85) that has no rudder pedals. I've read various stories about people taking a checkride in such an aircraft having a restriction on the license and having to take another checkride in a different aircraft to have the restriction removed. I've also seen this referenced as a myth that does not happen in real practice.
My questions:

Does this restriction really exist, or is it a myth?
Does it depend on the examiner?
Does it apply to sport pilot (where I would have to have an endorsement for another model anyways), or just private?
Would I have to take another checkride to have it removed, or could
it be removed with a CFI's endorsement?

I don't know the answer, but what I would say is you should get at least some training in an aircraft with rudder pedals. Using pedals is a very important skill, and without training it would be unwise for you to fly anything besides coordinated aircraft, and those are few and far between.

@GdD: I've also had some training in a J-3 with rudders, so I won't go completely without that aspect of training--just the majority of it will have been in the ercoupe, so it'd be best for me to take the checkride in it. After I get my sport pilot license, I do plane to continue on to private and will likely train in a cessna--but in the mean time, I'd like to know if I will be restricted to an ercoupe if the opportunity arises to fly other LSAs. Thanks!

I don't keep up with the Light Sport world much, but I was under the impression the dumb "endorsement for each make and model" thing for sport pilots had gone away and you can fly any LSA-eligible aircraft in the category & class for which your certificate is issued -- Did that not happen?

The restriction you're talking about does exist, but there's no explicit wording for it. It's described in FAR 61.45(b)(2):

An applicant for a certificate or rating may use an aircraft with operating characteristics that preclude the applicant from performing all of the tasks required for the practical test. However, the applicant's certificate or rating, as appropriate, will be issued with an appropriate limitation.

One of the most fundamental tasks in the Sport Pilot PTS is maintaining coordinated flight (you won't find it as a discrete task, but if you look at the PTS the phrase "while maintaining coordinated flight" occurs multiple times), and an Ercoupe without rudder pedals relieves the applicant of that responsibility because the aileron/rudder interconnect basically does it for you.
I'm not sure exactly how this works for Sport Pilots, but as you cannot demonstrate to the examiner that you can "maintain coordinated flight" they could reasonably apply the same restriction to your Sport Pilot certificate as they would to a Private Pilot certificate ("Limited to aircraft without rudder pedals").  You would need to demonstrate to a DPE or Examiner that you can operate an aircraft with rudder pedals at some later date to remove the restriction (it is a restriction on the certificate so the only way to remove it is to have the certificate amended/reissued/replaced).

The easiest way to avoid the entire issue is to prepare for and take your practical test in an aircraft with rudder pedals. You can do everything in the Ercoupe and then switch to the Cub for a week to brush up on systems and polish your maneuvers in that plane and get used to using your feet.

This is all good advice, I'd add to that switch to the cub for the rest of your training if that's what you're going to test in. Go back to the ercoupe later.

@GdD If the Ercoupe is substantially cheaper it may make sense to knock out part of the training in that plane - generally though I agree: Train in the plane you'll be doing your checkride in (or at least the same type of plane).


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Are there other examples of human-electric hybrid aircraft?
Has there been a human-electric hybrid aircraft after this. A more streamlined design; maybe capable of soaring as well...

Welcome! What do you mean by human-electric? it seems more electric than human powered... anyway the descendant of the Gossamer Penguin has been the Solar Challenger, another solar powered aicraft. The predecessor of the Penguin was a human-powered aircraft, the Gossamer Albatross. Aaalbaatrooossss...!

Yes. I assume by hybrid you mean that propulsion is provided by a solar-powered electric motor while the control system is powered by a human pilot.
From Paul McCready came Solar Challenger in 1981, certainly less flimsy than the Gossamer Penguin.

Solar Challenger (picture source)
In the same year, Solair I flew for the first time, followed by Solair II in 1998. Both were built by Günther Rochelt, who also built human powered aircraft.

Solair II (picture source)
Rochelt's Musculair 2, the fastest human powered aircraft until today, inspired Eric Raymond to build Sunseeker in 1990. Sunseeker II improved on those designs again, still using the layout pioneered by Musculair 2. It flew first in 2002.

Sunseeker (picture source)
Icaré 2 was based on glider technology and flew first in 1996.

Icaré 2 (picture by Uli Reinhardt, Zeitenspiegel (Zeitenspiegel) [CC BY-SA 2.0 de, GFDL or CC-BY-SA-3.0], via Wikimedia Commons
With Sunseeker Duo the first solar-powered two seater flew in 2014.
For a comprehensive history of solar flight see here (PDF), and for some more background see here.


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Could an inflatable wing be installed on a Silent glider aircraft?
Would it be technically feasible to install the Pneumagic inflatable wing on the Silent glider?

Here are some of my thoughts. I'm not fully convinced about the tradeoffs though, which would require a little more work to figure out if it was beneficial:

The wing appears a lot thicker in the article than in the silent glider, adding more drag than the solid wing which it currently uses. To get it as thin would be challenge, since the article suggests that the benefit of adding pressure is marginal for the same wing, so you could only make it thicker. In an convential design, the fabric can be a lot thinner than here were it's got to hold a lot pressure. I'm sure you have to add metal wires to maintain the shape under load, adding a weight penalty.
Using a pure air-based system, I'm also somewhat unconvinced about the 'responsiveness' at the controls, since You'd only be transferring the loads at a single point into the (flexible) structure, rather than across an area as in the article example. An analogy of this is to think of trying to apple a torque force to the center of a pool noodle in water, and to observe the ends relative to the center. You might end up having to make a rather extensive wing root structure to make this work.
The benefit would be portability, but since the silent glider has an engine, this would probably not be of a huge concern, since you could get it where you wanted it.

My verdict: It could probably be done, but I'm doubtful about the performance benefits. Then again, I'm only a first year aerospace engineering student, so you're welcome to come with thoughts and any criticism :)

"trying to apple a torque force to the center of a pool noodle in water,"....  What???  :-)

http://www.energykitesystems.net/Lift/2011/2011janLIFT.html
These people are trying to build a backpack-able 55lb ultra-portable glider.
These are NASA's inflatable wings.
https://www.youtube.com/watch?v=4SBi9Bffbb4#t=262
Do you thing something equally rigid could be used for gliding. And what is the difference, in material, between this and the Pneumagic.

@AyanMullick The problem which I primarily see strapping it onto the silent glider is that there is a large increase in weight by adding on an engine and fuselage, which would require it to be a thicker or faster, but I'm pretty sure it could be done, but the benefits would maybe not great. The structure dosen't seem to have a great glide ratio, since the surface isn't smooth. The main difference between the two aircraft appears to be the air pocket structure size. principle is the same.

@Manfred For the sake of portability,is there any inflatable wing available or in the making that would adequately replace the rigid wing of the Silent Glider ?

@AyanMullick I don't think so. The inflatable wing dosen't seem to have developed yet even in unpowered cases so at the moment, I don't think so. you might be able to get a wing though which detached and folded in two to fold in flat again the fuselage to save space, like can be done with many conventional (stiff) glider wings.

@Lnafziger. apply :) And a pool noodle I guess is this: https://www.google.com/search?q=pool+noodle&um


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Do you need clearance from ATC to switch to a different approach at non-towered airport?
When coming in on an instrument approach at a nontowered airport, the approach/center controller will clear you for the approach and approve your frequency change to the CTAF.
Once you're cleared for a particular approach and have changed frequencies, if you later decide you need to deviate from the planned approach (i.e. sidestep or circle instead of straight-in) do you need to get a revised clearance from the approach controller or is clearance for sidestep or circling implied?

One important reason that you can't just switch to another approach yourself is that if you have to go missed then the controller needs to know where you're going to go. If the controller clears you for the ILS approach and you end up going missed on the RNAV approach, that could create problems with separation because you aren't where the controller expects you to be.

Quoted from the Instrument Procedures Handbook, page 4-6:

APPROACH CLEARANCE
The approach clearance provides guidance to a position
  from where you can execute the approach, and it also
  clears you to fly that approach. If only one approach pro-
  cedure exists, or if ATC authorizes you to execute the
  approach procedure of your choice, the clearance may
  be worded as simply as “… cleared for approach.” If
  ATC wants to restrict you to a specific approach, the
  controller names the approach in the clearance—for
  example, “…cleared ILS Runway 35 Right approach.”
When the landing will be made on a runway that is not
  aligned with the approach being flown, the controller
  may issue a circling approach clearance, such as
  “…cleared for VOR Runway 17 approach, circle to land
  Runway 23.”

So if they name the approach, you are restricted to that approach.
I searched the rest of the book for items specifically related to non-towered operations, and found nothing that contradicted that.

For what it's worth, the ATC Order specifically prohibits ATC from clearing a pilot for circling approaches at non-towered airports:  4-8-6. CIRCLING APPROACH a. Circling approach instructions may only be given for aircraft landing at airports with operational control towers.

I can't find anything in the IP Handbook or other sources to back me up, but I believe this to be incorrect: the pilot can choose to circle-to-land or sidestep provided those are allowed (with published minimums) for the approach you're cleared for. As Lnfagziger said, ATC cannot authorize this -- because it's up to the pilot. It really doesn't matter to ATC: they will not clear any other aircraft for an approach to that untowered airport until you report you're on the ground or cancel your IFR.

@dvnrrs after doing some research, I came to that conclusion as well. Perhaps you can post an answer to that effect?

@newmanth I wouldn't make it an answer without a reference to back it up... if you have a source you can answer your own question though. There's even a badge for that. I'd upvote an answer with citations.

@dvnrrs unfortunately, I can't find any references either! In fact, other than the ATC Order that Lnafziger referenced, the FAA appears silent on the subject. So... is it one of those things where if it isn't prohibited, it's allowed? :P

In the Center environment, at a non-towered airport, if you're cleared for a specific approach, that's what is being protected, including circling, and the missed approach.
There is no provision for a pilot to change the approach without contacting ATC.
Also, controllers do not clear for "circle to land", or any other runway "landing" clearance at non-towered airports, because we cannot see the runway.
Any clearance at an non-towered airport that includes the phrase "cleared to land" or "circle to land" is incorrect for that reason. Let the buyer beware.
We see this primarily with former terminal controllers that have transferred into the Center.

+1. In the terminal (radar) environment, for a non-towered airport, everything you said also applies: Aircraft are cleared for a specific approach, and may not execute a different approach (before or after the missed approach point!) without receiving an amended clearance. But they may circle to land on any runway, as long as they comply with the appropriate circling minima. An approach clearance is not a landing clearance and "ATC gave me this straight-in approach" is not an excuse for colliding with opposite-direction traffic.

@randomhead, you're  alright. Come on out to ZDV, sometime!


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Does the rudder need to be held throughout a coordinated turn?
It's widely known that to perform a coordinated turn, rudder must be turned as well as ailerons. My question is what to do after the desired bank angle is achieved?
In the Airplane Flying Handbook we read:

After the bank has been established in a medium
  banked turn, all pressure applied to the aileron may be
  relaxed. The airplane will remain at the selected bank
  with no further tendency to yaw since there is no
  longer a deflection of the ailerons. As a result, pres-
  sure may also be relaxed on the rudder pedals, and the
  rudder allowed to streamline itself with the direction
  of the slipstream.

So does that mean that the pedals will remain in "shifted" position as a result of the rudder remaining slightly turned?
I also wonder how this is imitated in simulators (I'm using FlightGear) as all (even expensive) simulator pedals return to "zero" position themselves?

Step on the ball! (Go up and try the maneuver, paying attention to the ball on your turn coordinator. If the ball remains centered, leave the rudder wherever it is. If the ball is to the right or left, apply right or left rudder accordingly. Only do this from a safe altitude and after clearing the area, and don't keep your head inside the cockpit too long without doing a proper visual scan outside!

Here's an interesting read (but far beyond the scope and level of the question ) --https://aviation.stackexchange.com/questions/31440/does-slipping-in-turns-allow-higher-climb-rates/31453#31453

Feet aren't that sensitive to position.  To a first approximation, having the rudder pedals center themselves with springs is fine for the simulator.  The rudder would only tend to be very slightly offset during a feet-off-rudder turn, since the vertical fin tends to streamline itself to the airflow.

I'm not sure I agree with the statement that an aircraft will remain in a turn with neutral aileron; I would expect any airframe designed for "positive stability" will tend to roll out of a turn on its own, if only slowly. To maintain a turn, at least some control force is required.

When you deflect the ailerons, you increase lift on one side of the wing and decrease it on the other. This causes a parallel increase of the local induced drag where lift is increased and vice versa. The consequence of that is a yawing moment which needs to be corrected with rudder deflection.
Once your ailerons are neutral, this yawing moment goes away, but now your airplane is in a constant yawing motion which increases airspeed on the outer wing and swings the tail around, so your vertical tail sees some sideslip even if your ball is centered. The airspeed differential between inner and outer wing causes some friction drag differential which tries to pull the aircraft out of the yawing motion. Depending on the tendency of the rudder to follow a sideslip, you will need some pressure to keep the yawing motion going.
It is hard to be more specific, because details depend on the particular airplane.
In most of the airplanes I have flown, you also need to keep some aileron deflection to keep your bank angle constant. Here are two effects which go against each other, so again the details depend on the particular aircraft. One effect is caused by the airspeed difference which causes a lift difference between inner and outer wing. To correct this, you need to deflect the aileron against the bank. The other effect is caused by the different centrifugal forces of the masses of the inner and outer wing. The whole wing is moving at the same angular velocity, but centrifugal acceleration is the product of the square of the angular velocity and the radius of your motion. Since the outer wing flies at a larger radius than the inner wing, the masses of the wing will try to pull the aircraft level. This needs aileron deflection into the bank. If you are lucky, both effects cancel each other out, but normally they don't.

Originally my question was about some light aircraft (e.g. Cessna 172). It's quite clear for this plane how airflow is able to "shift" pedals during the already established turn via strings going to rudder itself. But what about say B777? Is airflow strong enough to override hydraulics that is holding the rudder in "straight" position after the pilot returns pedals to neutral position and releases any pressure on them?

@HUB: No, on an airplane with hydraulic actuation the actuators are by design strong enough to hold the rudder at any position within the envelope (full deflection up to vA, 1/3 deflection at vD).

@PeterKämpf: Don't the pedals have feedback? I believe they do. I don't know how the yaw damper command is added though.

@Jan Hudec: If you stand in the pedals, you will feel that the rudder floats into the circle, sure. I do not now about FBW designs; I would guess the pedals reflect the position of the rudder and all pedal force the pilot feels is generated by springs. Plenty of pilots do not have their feet on the pedals, so creating fancy feedback systems is a waste. The force the pilot feels is proportional to the aircraft's yaw stability, so having some feedback is actually quite useful.

@PeterKämpf: Airbus does not have FBW for rudder. It has direct hydraulic link (and therefore normal feedback) so rudder (together with elevator trim) can be used even in case of total electric failure. It has good enough yaw damper to take care of coordination in turns though, so pilot does not need to touch the pedals most of the time.

@HUB: So the pedals with hydraulic actuation work just like in light aircraft except the force is scaled.

@PeterKämpf: Also note, that there are no FBW designs where force would be generated purely by springs and position of the control element corresponded to position of the control surface. Airbus side-stick is spring-loaded, but it's displacement corresponds to the pitch and roll rate of the aircraft, not position of the surfaces. And Boeing FBW simulates the mechanical link.

For what it may be worth, in 747-100 and -200 aircraft, operationally with all engines operating, you take your feet off the rudder pedals after liftoff and don't put them back on until short final. The yaw damper handles (by way of the hydraulics of course) all adverse yaw including any in a sustained bank.

As an example, consider the Automatic Flight Control System (AFCS) of the A7-E. The A7-E is a Vietnam era light-attack jet that was deployed until being replaced by the F-18. I suspect that the system used to maintain coordinated flight hasn't changed much since then.
The AFCS is a 3-axis autopilot with control augmentation. It includes automatic pitch trim, failure monitoring, with automatic disconnect and warning. There are 8 operational modes:

Yaw stabilization
Control augmentation
Attitude hold
Heading hold
Heading select
Altitude hold
Automatic carrier landing system
Ground controlled bombing

The operation of the AFCS required both electrical and hydraulic power.
The yaw stabilization mode provided coordinated turns, with an aileron-rudder interconnect, and provided up to 5 degrees rudder trim in either direction. The coordinated turn was automatic, without pilot input. The yaw computer got its signal from a lateral accelerometer, and movement of the rudder pedals placed this signal on hold. As previously noted, once airborne you kept your feet off the pedals. A pilot could engage and disengage the yaw stabilization mode.
I went to maintenance to read the maintenance log book on the aircraft. I had a launch, and was on my way out to the flight deck. This is from my memory of over 30 years ago, but nonetheless it is fairly accurate. There were pink slips and yellow slips. Pink slips were maintenance problems that had downed the aircraft at some point. I would read these to get an overall idea of the problems, recurring and otherwise. Yellow slips were, "Hey, keep an eye on this. We haven't downed the aircraft, but ..."
The mission included unusual attitudes, and low speed flight, common in air-combat maneuvering. I looked over the log book and noticed the AFCS had a yellow sheet, and stated that the system had initiated abrupt rudder control inputs at a point in a previous flight. It was yellow because maintenance was not able to reproduce the problem. I didn't connect the dots, although you might have.
I didn't think too much of the yellow sheet because I never had problems with the AFCS system. Additionally, it was automatic and so I rarely interacted with it except for hitting the switch that engaged it.
In the dog fight I ended up on my back with 0 airspeed at around 20,000 feet. The AFCS inadvertently commanded an abrupt rudder input. A departed aircraft, with a yaw input, are the conditions necessary for a spin.
And spin I did.
The AFCS yaw stabilization is great for allowing the pilot to concentrate on other tasks other than looking at the turn needle, like looking for the enemy at your 6. One must always remember, though, that automatic systems are often clever by one half.

Nice reading! Thanks for sharing..

How much rudder input you need during a turn depends on the aircraft. As long as the ball is out of center, there is lateral force on the aircraft because it isn't going in the direction it is pointed and there is a lateral component to the relative wind acting on the fuselage. For some aircraft, a bit of rudder will be needed throughout a turn; for others, rudder is needed as the turn is initiated but the rudder input can be relaxed until you roll out of the turn when you may need a bit of opposite rudder.
As far as centering behavior of the rudder pedals, I think the pedals on most aircraft will tend to center themselves due to aerodynamic forces on the rudder. When the aircraft is sitting stationary on the ground, the pedals may stay where they are left. Many aircraft use the rudder pedals to steer the nosewheel (which is typically set up to caster), making pedal feel somewhat variable, depending on whether the aircraft is on the ground or in the air, and how fast it's taxiing or flying.

Old question, but relevant to new readers.  This is a question you ask someone who has actually flown the type of aircraft you are interested in. There is no general rule because of differences in wing and tail design.
A high wing dihedralled aircraft will need significant rudder and aileron inputs while turning,
but a low wing "warbird" type designed to fly right side up, inverted, on its side etc. has much less built in "righting" properties and there for will much more readily hold a bank when rolled,  hence the term "bank and yank" (elevator).
Rudder does generally help coordinate the turn as the faster outside wing has more drag.
But again design comes into play.  Vertical tail area will help yaw the plane into the turn with or without additional rudder.  So it is possible to "slip turn" the plane, as airliners do.
As far as rudders "remaining in the shifted position" believe me, you will move them if the plane isn't doing what you want it to.
So the rudder, as with all controls, is there if you need it.  So are qualified instructors.
Take a lesson in your type, it will be well worth the investment.


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Why do drones near airports necessitate cancelling flights?
From Wikipedia's page on the Gatwick drone incident:

Between 19 and 21 December 2018, hundreds of flights were cancelled at Gatwick Airport near London, England, following reports of drone sightings close to the runway. The reports caused major disruption, affecting approximately 140,000 passengers and 1,000 flights.

I assume that drones can crash into aircraft, negatively impacting the safety of flights.

Suppose airport staff report sightings of a drone. What should the airport do?
Is this considered an emergency? Why or why not?
Can other planes request clearance to avoid the area?
Have any documented instances of drones resulting in injury to or loss of crew, passengers, or plane?

I think you have your own answer already.  Break a window, damage a wing, damage a control surface, damage an engine, all leading to an impact on safe landing.

@CrossRoads Have their been instances of this? Or is it purely theoretical? There's (2) similar questions on laser, and I'd like to know more, except about drones.

@CrossRoads The question is now edited. What do you think?

See this article on drone suspected in helicopter crash  http://fortune.com/2018/02/16/south-carolina-drone-helicopter-crash/  Besides the headline, the article also discussed 4 other drone related events.

Possible drone collision with a 737 in Mexico: https://www.bloomberg.com/news/articles/2018-12-13/aeromexico-737-jetliner-damaged-in-possible-midair-drone-strike

@CrossRoads Thanks for the link! It definitely covers part of the questions.

@StephenS The picture of the nose of the aircraft makes me cringe... What if the drone had hit somewhere else? Would the impacts have been more negative?

Re the title question, a plane hitting a crow is enough to take out an engine, as shown in the following video.

Crows weigh about 500–600g. A drone such as a DJI Phantom weighs two to three times as much and isn't nearly so squishy.

Interesting! Thanks for the new perspective!

@TomMcW They will halt operations if there are flocks of birds hanging around the runways. But the main distinction is that birds can be trusted to fly around more or less randomly, informed by self-preservation; they also mostly don't hover in one spot, so each individual bird is a transitory event. You already know that somebody flying a drone around an airport is an a-hole and you have to take into account the possibility of it being deliberately flown at planes.

@TomMcW there's also maliciousness - imagine that same drone carrying gunpower or ball bearings or a bag of flour targetting an engine intake.  Or paint on the windscreen.

When I first read this, I thought it said "a plane hitting a cow is enough to take out an engine."


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Is a 5 hour 3 session process normal for a plane checkout you're already trained in?
I've joined a flying club and am in the checkout process for their 152. I've trained in it, was endorsed by a 20,000+ hour instructor (who felt comfortable enough renting his personally owned 152 to me after the checkride), and my DPE (who a commercial pilot tried to steer me away from due to her supposed high fail rate, i.e. she's demanding) thought I flew the plane well. I'm a very new VFR pilot with about 70 hours total, and find this checkout process is taking longer than usual under these circumstances. Has anyone gone through a similar situation? How have they dealt with the matter? The instructor is also making me feel less safe as a pilot doing things like banking with full flaps, and pushing "flap religion" on me (i.e. 10 on DW, 20 on base, 30 on final without really considering the approach environment). Due to W/B restrictions on the 152 he's the club's only viable checkout instructor.

Does not sound appropriate to me.

Yes 5 hours is very long.  Either you are a very marginal new pilot, the instructor is incompetent, or the club is a "time whore", running up hours because they are desperate for revenue.  Before your departure, does the instructor sit there discussing something or briefing something with the engine idling, letting the Hobbs tick away?  All chit chat should be completed before engine start, then fire up, taxi, runup, and go.

@JohnK That isn't always the case. For example our club requires 20 hours of dual instruction in the aircraft prior to being signed off if you don't have at least 100 hours PIC and time in a 177. If you have 100 hours we reduce it to 10, but we aren't doing it for money, it keeps our insurance costs down. This isn't the OP's case, but for our club taking somebody in who fly's 172's can be a significant change to flying the 177. Some members combine the requirement with some IFR training to kill two birds with one stone.

Find another club.

@RonBeyer I get it that a good deal of hours is required if I step up to say a 172 with AP and esp. a difficult complex plane like a Mooney, but we're talking about a stupid simple VFR 152 here. It's not so much the time also, it's the time and effort to "unlearn" his instruction immediately after being checked out.
Yes, the CFI is kind of chatting it up a bit on the ground as we're idling. It's a busy class G airport and proper CTAF/traffic avoidance is necessary, I get it. Just that we take FOREVER to get airborne.

I would expect that a new pilot starting at a club already trained in the affected airplane would get what amounts to a proficiency check plus a bit of indoctrination in club specific procedures and techniques to the extent that they have them.  Mayyybeeee 2 hours...  @saigafreak, DON'T let instructors do that.  Insist on ground briefings being complete prior to start.  Aircraft engines are warm enough to fly in a couple minutes.  You are paying close to 2 bucks a minute to listen to a guy yap.  You might as well sit out on a picnic table setting dollar bills on fire.  They are milking you.

It is normal for flying clubs and flight schools to require a checkout before allowing a renter to solo, which may take several hours, regardless of their license level or previous experience. They often require additional training if you dont have a certain minimum time in type.
Your club might be slightly more paranoid than average, but that probably translates to cheaper club insurance and thus lower rental rates, which means you will probably save money if you stick around.
Also, it should be noted that 70-200 hours is the period with the highest accident rate, so some paranoia on their part is probably justified. Even if it's "just a 152."

A five hour, 3 session checkout process does not seem appropriate for a Cessna 152.  You'll have to look at the savings you hope to gain by doing your flying with the club, and decide whether it is worth it for you to continue.  It would help if your question stated whether or not this lengthy checkout process was specified from the outset-- what was your initial expectation when you decided to check out in the aircraft?  What sort of checkout procedure have other pilots been subjected to?  Since we don't know how you fly, ultimately it is impossible for anyone to say whether or not anything inappropriate is going on.  Maybe the instructor just has a different "style" of flying from you and since you are not really in a position to debate anything, you may just have to adapt even if it does take some time.  As long as you are continuing with the process, you might as well try to learn something useful from the training, even if you don't fully agree with all aspects of your instructor's approach. At any rate, you should discuss your concerns with the club leadership.  If enough people give the same input, some change might happen.
Or find another club.

I guess this is the best objective answer I can expect. Right now it's been 3 hours but we are expected to spend at least 2 -2.5 more hours, PLUS 1 hour of ground instruction on the written quiz, about 8 hours paid ground + flight instruction in total. Yes, the club rules are strict and my PPL CFI warned me about joining them, my friend w/same PPL CFI and was a former member did also. They have a nice organized layout as a club and that's what brought me in, but I feel trapped now in some purgatory state. There are precious few clubs in my area but I may explore them more now.

@saigafreak so you were warned, not once, but twice... well, anyway, you're allmost halfway done, so why not just stick with it and see how it turns out. Unless the warnings you got were about the club in general, not just the checkout process.


text:
61.39 (a)(6)(i) CFI applicant checkride question
I am taking my CFI checkride on 6/30, the very last day my 2 calendar month endorsement was granted (4/26). In the event the air portion of the checkride cannot be completed by that day and we go up on 7/1 to finish, does the 2 calendar month endorsement still hold since when we began the practical test and endorsements were verified?
For CFI-A there doesn't seem to be any minimum amount of time required 2 calendar months prior unlike say a PPL which is 3 hours dual given 2 calendar months prior. If he has to add another endorsement to be safe, can we just do a little bit of ground and call it a day?

Yes. Sorry, I was referencing what my logbook states (a123) but (a6i) is really what it pertains to wrt 2 months


text:
Is there an FAA rule or Advisory Circular with regard to blood donation?
Is there an FAA rule or Advisory Circular with regard to flightcrew member blood donation?  For example, how many hours or days is required or advised before a pilot may act as a crewmember?
I'm interested in finding the source of legitimate FAA policy or guidance for flightcrew members.  If the answer is, there is no FAA rule or advisory circular, I'd also be interested in specific examples of FAA-approved air carrier policy.
It seems 24 hours is the generally accepted waiting period to recover from possible hypoxia related to a donation.

The Pilots Handbook says, "Hypemic hypoxia can also be caused by the loss of blood due to blood donation. Blood volume can require several weeks to return to normal following a donation. Although the effects of the blood loss are slight at ground level, there are risks when flying during this time."

This link gives some guidelines, https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item48/amd/bd/ 24 hours for blood donation, 4 hours for platelets. I always wait until the next day after donating platelets since I’m slightly allergic to the sodium citrate that they use as a thinner and it wears me out.

lukecolli98 contributes: For a PPL holder under EASA/CAA, it's 24 hours (source: Pooley's Air Pilots Manual, book 6). He believes it is longer for commercial operations.

An air carrier that I have worked for specifically addresses this issue in their General Operations Manual—which is accepted by the FAA. The manual gives the following requirement:

Flight Restrictions After Blood Donations
Flight personnel shall not participate in any capacity as flightcrew members for a period of 24 hours after donating more than one-half pint of blood.

Note that this portion of this manual is accepted by the FAA, not approved.1
One unit of blood is generally 470-500 mL, or one pint. The one-half pint specified above half of a regular unit of blood.  According the the Red Cross, a typical donation is about one pint, or one unit.

The FAA also publishes the Guide for Aviation Medical Examiners. I am not an AME, nor am I fully familiar with the Guide or how to interpret it. However, I understand that the following table shows that outside the listed time-frames, an applicant for an airman's medical certificate could be considered medically fit for flight duty:

1 The terms Approved and Accepted mean specific things to the FAA. See 8400.10, Vol 3, Ch 15, Sec 1:

Approved: When approved is used to describe a document, manual, or checklist, it means that a regulation requires FAA approval and that the FAA has evaluated and specifically approved the document, manual, or checklist.
Accepted: Accepted is used to describe a document, manual, or checklist that does not have, or is not required to have, FAA approval. Only a portion of an operators manuals are required to have FAA approval. The remaining portions are accepted by the FAA. Operators are required to submit the entire general manual to the FAA for review. If the FAA concludes that an accepted section of the general manual is not in compliance, the FAA must formally notify the operator of the deficiency. Upon notification, the operator must take action to resolve the deficiency.

Great.  @DawnBreaker found this Ultralight AC: AC90-89B.

There is no 14 CFR (FAR) or Advisory Circular that requires a set wait time between giving blood and flying.  The closest thing is a recommendation in a handbook for ultralight flight testing. Where it recommends not flying for 24 hours if giving 1 unit of blood (500ml) or less and 72 hours if giving more.
Now of course if you do fly during those time periods, be aware that you might get hit with the FAA's favorite catch all 14 CFR 91.13 Careless or reckless operation instead. (Though a decent aviation lawyer might could get you off pretty easy on this charge.)

AC90-89B is a great find.  It seems ironic to find that advice in the realm of  ultralight aircraft vs commercial operations.

From what I know, for crew members are prohibited from donating blood unless a period of 72 hrs has elapsed from the time of donation until the next scheduled duty flight.
Source : Regulation of the CAA (South African Civil Aviation Authority which follows FAA requirements and regulation)

This answer gives interesting information, but should be a comment since this question is asked exclusively about the FAA.


text:
Why was the Bristol Brabazon scrapped?
According to Wikipedia, 6 million pounds were spent developing the Bristol Brabazon, and the only prototype was scrapped for 10,000 pounds, that is a 0.17% loss recoup. There was a lot more value in keeping that plane intact than scrapping it, maybe for future projects, or special assignments, or further testing, like an An-225. It held more value as a museum piece, or a "sculpture" in Bristol, than the value from the scrap metal.
Was there a reason for being scrapped, other than the 10k in scrapped metal?

This was right after WWII (1949) so economies were still recovering

UK need huge amount of metal for reconstruction after WWII, they just scrapped everything even for the most well known warships

You're right, as an exhibition piece it would had been quite an attraction. But it was not up to the Bristol company to decide her fate.
During and after the war, most British aviation development was managed by the government. The Brabazon was the result of a committee which set the goal to develop a transatlantic airliner with 1943 technology, not by a company and its technological visionaries. If you had asked people like Willy Messerschmitt in 1943 how the future airliner would look like, he would had basically described a Boeing 707: Swept wings, turbojet engines, pressurized cabin for about 100 passengers. But Government bureaucrats put the goal for the Brabazon quite differently, and the result was technically obsolete by the time it took to the air. Even before the Brabazon flew first on September 4, 1949, the de Havilland Comet had already flown on July 27, 1949 and was on its way to revolutionize air travel. Its development had started later and was directed by engineers, not bureaucrats.
When that became obvious, the bureaucracy felt too embarrassed to keep the Brabazon around. The situation was similar to Beechcraft and the Starship: Burt Rutan's 85% scale prototype was cut into pieces out of spite when it became eventually clear even for Beechcraft's board just what a turkey it was. The same fate befell the Brabazon.
But its legacy for Bristol is still very positive - without the Brabazon, it would certainly not employ as many people in aerospace as it does up to this day.

why would there be more value in keeping it than in scrapping it? That's simply not true.
The ONLY value would be for a few aviation enthousiasts who might be willing to pay the entrance fees for a museum where it would be put on display.
But at the time there was a glut in aircraft to put in museums. And of course most British museums at the time (and many even today) didn't charge admittance, they were run as public services for educational purposes.

In a country with massive debt, recovering from a long and costly war, where raw materials are scarce, and aircraft to show off to the public are a dime a dozen, scrapping something that has no purpose and contains tons of valuable metals and other materials is the best thing to do, aviation buffs 70 years later who'd like to look at it and marvel at the folly of designers long ago to think something like that would be the future be darned.

I would compare it to the Spruce Goose. Still around, still attracting the crowds. Putting the Brabazon on display would had worked, maybe not spectacularly, but enough to earn it its upkeep. And the folly was on the side of the Government bureaucrats; the designers all achieved their Government-mandated goals.

@PeterKämpf except the Spruce Goose used non-strategic materials AND is and was private property rather than government property. And even then it barely escaped the scrappers, more than once. Even after decades of being a museum piece people were planning to scrap it because it was too expensive for them to maintain and they couldn't find a buyer quickly.

You should also consider maintenance costs. Keeping the airplane will surely cause some kind of cost and the maintaining party has to cover them somehow. Even if you have museum admissions or the like you still must have it running well enough to cover the quite high costs of keeping your airplane together.
That they did not keep it for further research indicates IMHO that the plane was simply not seen as a good fundament for further research.
I am very sure that the people in charge back then did consider carefully what they do with it. For some reason they would rather write off almost 6 mio and get the money for the scrap metal. Even though mistakes happen a lot, I think that they knew what they did :)


text:
What is the pressure in a civil aircraft fuselage at flight ceiling?

What is the pressure (in bar) in the fuselage at flight ceiling of large passenger airliners?
Is this pressure the reason for the difficulty in having large windows? If so, how can the window size be increased?

The second question is basically a duplicate of What are the factors behind increasing aircraft window sizes?.

The pressure inside the cabin is usually more than the outside pressure at the cruise altitude. The pressure altitude (ISA altitude with the same pressure) inside the cabin of civil aircraft is called the equivalent effective cabin altitude or normally cabin altitude.
As the aircraft climbs, the cabin altitude is gradually raised so that it reaches around 8000 ft for the aircraft cruising altitude of ~40000 ft. This level is maintained at flight ceiling too.

Source: www.flyertalk.com
The pressure is around 0.75 bar inside the cabin. The outside pressure at this point is around 0.2 bar, resulting in a pressure differential of 0.56 bar. This pressure differential causes stresses on the aircraft body.

Source:ecnmag.com
In addition to the stresses, pressurization - de-pressurization cycle can cause fatigue in the windows.
As reducing the cabin altitude will improve the passenger comfort, newer aircraft tend to have lower cabin altitudes. For example, the Boeing 787 has a pressure altitude of around 6000 ft and the Bombardier Global Express jet has a cabin altitude of around 4500 ft.
This is achieved by the use of advanced composite materials, which allow a higher pressure differential and have excellent fatigue properties compared to the metals. As a result, the windows of newer aircraft are considerably larger than their predecessors.

Image: Boeing

"The pressure inside the cabin is usually more than the outside pressure at the cruise altitude." Usually? You mean, "when something doesn't fail catastrophically?"

Could someone please tell me the exact origin of the cabin pressure graph? I would like to cite it and www.flyertalk.com only is not helping that much.
Thanks a lot!

@DanielBaltazar the source appears to be thos thesis on researchgate, DOI:10.13140/RG.2.2.25957.01764

What is the pressure (bar) in the fuselage at flight ceiling of large
  passenger airliners?

Aircraft are typically pressurised to an equivalent altitude of 1800m (0.815 bar) to 2400m (0.750 bar). Be aware this is absolute and not relative to the atmosphere around the plane.

Is this pressure the reason for the difficulty of having large
  windows?

It is the most important reason. When stuff is not pressurised you can pull off fairly decent stunts, like the huge mirror on the SOFIA aircraft for instance.

What advancement would be a game changer and allow large windows?

Composite materials are currently the big deal and bringing considerable benefits (See this question). If you can skip the material change entirely, by using a thing such as transparent composites, then you can make them any size you please.


text:
Why do aircraft use hydraulics instead of pneumatics?
I was reading about how the F-35 is having trouble with the "fueldraulic" system. This made me wonder:

Why don't aircraft use pneumatic systems instead of hydraulic/fueldraulic systems?

There are several advantages of pneumatic (compressed air) over hydraulic (pressurised liquid) or fueldraulic (pressurised fuel) systems:

No need to carry hydraulic liquid. That saves weight and maintenance cost.
Half as much piping, as there is no need to return hydraulic liquid to the pump - compressed air can be released after use. That saves more weight.
Leaks are less dangerous. There is no danger of running out of hydraulic liquid or of leaking fueldraulic liquid catching fire.

There are disadvantages too: less pressure -- which means less power per unit of gas/liquid -- and less precision, as gas is compressible. But I feel like these problems should be solvable in a modern computer-controlled aircraft. So what's the problem?

I guess you nailed it in your question. Hydraulics operate at 3000+ PSI so small tubes can be used. You would need tubes at a lot higher pressure to do the required work that you will have to continuously replenish by bleed air. Furthermore, there is huge lags everywhere due to the low speed of sound in air, and no matter how modern your control systems, there's a limit on how you can control things, called the 'waterbed effect'.

Aircraft do use pneumatic systems to power engine starts, the air cycle machine, wing anti-ice, pressurization, etc.  That it also has a hydraulic system should shed some light that it is needed since the pneumatic stuff is already there.

There are pneumatically actuated systems on at least some aircraft -- early 747s use pneumatic actuators for the LEDs, and some smaller aircraft have pneumatic L/Gs.

The big disadvantage here is the loss of precision due to the high compressibility of gas compared to liquid. Because gases are highly compressible, they provide a buffer to changes in pressure commanded by the operator to move the piston in the cylinder. That poses two problems; first, it means that the pneumatic cylinder doesn't respond instantly to pressure differentials, because the differential must first overcome the cylinder gasket's static friction. Second, it means that the movement of the cylinder is more easily opposed as long as whatever force opposes the gas pressure can overcome said pressure without causing whatever the pneumatic system is controlling to fail.
To overcome these shortcomings, most pneumatic systems run at very high pressures, so that the pressure differential between the two halves of the cylinder readily overcomes static friction and any other opposing forces. However, that creates another precision problem; high-pressure pneumatic cylinders are essentially two-state systems; the piston or actuator is typically at one or the other of its extremes of movement, and transitions between them very quickly as gas pressure is applied to one side or other of the cylinder.
None of these behaviors are desirable for aircraft controls; instructors labor daily to teach their students not to ham-fist the controls, instead using a bit of finesse to get the plane to do what they want in a smooth, controlled fashion. Why then, would you want to undo all that finesse with a control system that can only move the surface to the extremes of its travel?
Hydraulics, by contrast, allow a much higher degree of finesse. Because liquids don't readily change density, the pressure changes within a hydraulic cylinder require much more force to oppose, but by the same token, as the volume changes the pressure on the side being supplied with fluid decreases rapidly. This allows a hydraulic cylinder to be positioned much more accurately, regardless of any external forces acting on the system. The disadvantage is hauling a fairly heavy liquid up into the air, and having only limited capacity to replace it if any of it leaks.
Electrical actuators are a common solution to that disadvantage, especiually in light aircraft. Electrical actuators use an electric motor or servo to provide the mechanical action. These actuators can be controlled with a high degree of precision, and their "supply system" is just an electrical circuit, no heavy and complex hydraulic lines and cylinders. Their disadvantages are a tradeoff between speed of movement and maximum applied force while moving; you can either make an actuator that moves very quickly, or an actuator that will move no matter how much force is opposing the movement, but you really can't do both. They're still useful in light aircraft to control flaps (with a cable system used for the main surfaces), because they allow for precise amounts of extension or retraction, and don't have to instantly respond to input like the primary control surfaces do.
There is something on the horizon that could make pneumatics feasible for aircraft. Hydraulics systems were recently improved with the development of the electrohydraulic servo valve. This system uses a variable electrical potential (voltage) to move a hydraulic cylinder by a prescribed amount proportional to the voltage applied. Pure electrical servos have been around for decades, but the maximum amount of force available from a servo is insufficient for large airliners, while for smaller aircraft the servo motor's relatively high weight compared to simple cable controls is a disadvantage. The electrohydraulic servovalve concept is used in newer large aircraft to replace pure hydraulic or cable/hydraulic hybrid control systems, because the hydraulic system can now be controlled by an electrical circuit instead of hydraulic lines or tensioned cables coupled to the control column. This allows for "fly-by-wire" aircraft such as most Airbus airliners as well as most fighter jet designs of the last 40 years.
A similar concept is under development for pneumatics, allowing the precise placement of an actuator using pressurized gas in response to an electrical voltage. This would provide all the advantages of an electrohydraulic system, with considerably lighter weight and faster response, but still having the disadvantage that a significant opposing force could prevent movement of the actuator especially as it approaches the desired position. Whether that will be an issue in a large aircraft remains to be seen, and the weight savings of losing the hydraulic fluid might not be worth it, but if the tradeoff is acceptable, it would further increase range or payload of the next generation of passenger aircraft, with the added safety/reliability feature of being able to compensate for a slow leak in a pneumatic system by simply adding more air with a compressor pump.

+1 for having a detailed answer instead of lazily cramming it in a comment. Guilty as charged...

A pneumatic cylinder could probably be better than a hydraulic one in cases where the objective was to modulate force rather than position; if one were to design the control linkage for a control surface so that the force generated by the surface would be some multiple of an applied force, using pneumatics to apply that force would mean that if turbulence caused the force produced by a certain angle to change, the surface would move in response without the change having to propagate through the plane's control system.  In theory, nicer than hydraulics, but oscillations...

...are probably far harder to control than with hydraulics (if hydraulics move a control surface to a particular position, having it stay precisely where it is would cause the effects of turbulence to buffet the aircraft, but if it's not moving it can't oscillate).

@supercat exactly what I was thinking as a counterexample.  But in many applications oscillations like that would cause system failure.  There are too many disturbances occurring during the time the system is correcting for these oscillations.  Too many calculations and reactive inputs, never enough time or stability.

@BAR: Automotive suspensions have traditionally used hydraulics to control oscillation, but some newer systems are using more active controls.  I'm not sure to what extent such a thing could be useful on aircraft, or whether there's so much unavoidable coupling of turbulence to the fuselage by the main wing surface that having control surfaces move in response to changes in airflow would do little to improve the ride.

@supercat most turbine planes do exactly that automatically - move control surfaces in response to changes in airflow. The problem is if a component of the control system is inducing oscillations then this has to be corrected by the same control system... the same control system that will need correction for that last correction...

Pneumatics can be finicky about moisture/ice as well. You will find that aircraft that use pneumatics for some function (rudder boost/bias in Hawkers and some King Airs) they will have some sort of heating system (either bleed air or electric "muffs") to keep ice from forming.

it is said that every production tool designer's first automated assembly tool is pneumatic, after which he learns his lesson and never again designs a mechanism actuated by air.

One of the first reasons that comes to mind is air volume. Remember that a plane may be sitting on the ground on an 80 °F (27 °C) day, and take off and climb to 35,000 ft where temperatures of -50 °F (-46 °C) may be present. The air in the system would lose volume as it cooled off and would alter the position of the control surface (let's say flaps) with out any control input. Fluids are less susceptible to this problem. Granted this could be controlled, but it would still require a regulation system.
Leaks can also be easier to find in a hydraulic system since you can either

see fluid leaking out
put additives in that can be illuminated under certain lights

Pneumatic leaks are often found by rubbing soapy water on a joint and watching for bubbles (at least that's how I find them). Sometimes they can be hard to track if they are in awkward places.

The pressure differential is also an issue with the altitude change, though less of one considering the nominal operating pressures of pneumatic systems; at 50,000 feet, the pressure differential between "pressurized" and "unpressurized" sides of a pneumatic actuator is 14 PSI higher than at sea level. Now, if the system operates at 100 PSI anyway, this is fairly trivial.

There are ultrasonic devices for finding leaks in pneumatic systems. They are fairly expensive though. And of course the non-leak-related reasons are far more significant.

Yes of course (I am user12000 by the way :D) pneumatics are fast, cheap, and light but do not have good precision and you have to carry pressurized tanks called reservoirs (that means you need space) and you need to fill your reservoir (that means you need a compressor it means space again). When you compress air it heats up (it means a cooler system which means space again). You can use it again if you don't use it frequently and you want cheap and light. Hydraulics are heavy, expensive, can use high force, and have good precision. You don't need to use a compressor because its uses fluid it needs a pump. Pumps are to smaller than compressors and they produce less heat. You also need a small reservoir (reservoir is needed hydraulics because of protect the system from stress by expansion of fluid because of heat up of system or vice versa).

Yes what's the problem indeed. It has been done, without any problems, with all the advantages you mention and without your cited disadvantage of low pressure. This article discusses the fully pneumatic design of the F27 and F227. Air at 3,350 PSI has some mighty fast action, plus it has stored actuation power which a hydraulic system does not have. Hydraulics can deliver a high pressure at a low rate: the pump rate. Hydraulic accumulators store a bit of extra pressurised oil so the system can very briefly exceed the pump rate - only briefly though, and the accumulator is also required to dampen out ripple. High pressure air can be delivered at a huge rate, for a much longer time.
The F27 has manually driven flying controls: an aircraft this size can be fully controlled using these. For larger aircraft, the force required to deflect the control surface can be generated by an actuator working at 228 bar, whether hydraulically or pneumatically operated.
I've spoken with some of the designers of pneumatic systems when I worked at the factory that made these planes. The only real difficulty they experienced during the design and implementation phase was the design of the controllers, a servo valve for a hydraulic system gives less headache than one for a pneumatic system. Just an additional engineering problem to be solved with an appropriate feedback loop.
And now we can design for the least problematic controllers of all, for electric motors & drives.

This brake discussion is old, but I don't see any answer pointing out that the  787 has electric brakes. (But see 5th paragraph of answer by KeithS regarding small planes.)
From the 787 FCOM section 15:

Electric Brake System
The brake system is powered by four electric brake power supply units.
The brake pedals provide independent control of the left and right
brakes. Four Electric Brake Actuators (EBAs) are provided on each main
landing gear wheel brake to control the application of braking force
to the carbon disc. The EBAs are controlled by an Electric Brake
Actuator Controller (EBAC). There are four EBACs that control all
eight main wheel brakes, each EBAC controlling the brake force of a
fore-aft wheel pair.
Source: Document Number D615Z003-TBC October 31, 2007
Revision Number: 4 Revision Date: February 15, 2010

Of course, Boeing talks up the electrical systems on the 787. Here is what they say about the brakes:

One innovative application of the more-electric systems architecture
on the 787 is the move from hydraulically actuated brakes to electric.
Electric brakes significantly reduce the mechanical complexity of the
braking system and eliminate the potential for delays associated with
leaking brake hydraulic fluid, leaking valves, and other hydraulic
failures. Because its electric brake systems are modular (four
independent brake actuators per wheel), the 787 will be able to
dispatch with one electric brake actuator (EBA) inoperative per wheel
and will have significantly reduced performance penalties compared
with dispatch of a hydraulic brake system with a failure present. The
EBA is line-replaceable enabling in-situ maintenance of the brakes.
In general, electric systems are much easier to monitor for health and
system status than hydraulic or pneumatic systems; the brakes take
full advantage of this. Continuous onboard monitoring of the brakes
provides airlines with a number of advantages, such as:
Fault detection and isolation Electrical monitoring of brake wear
Ability to eliminate scheduled visual brake wear inspections Extended
parking times Because the 787 brakes can monitor the braking force
applied even while parked, the electric brakes enable extended parking
brake times by monitoring and automatically adjusting its parking
brakes as the brakes cool.

How do they work? Here is a clue from PPrune:

The motors supply torque through gear assemblies to the actuators,
which are rams driven by a jack screw. There is a latching mechanism
to limit over-rotation and back driving, minimizing the current
requirements for the EBS actuator motors.

espacially harnesses include mechanical, hydraulics, pneumatics and electromechanical parts. Generaly Aileron, elevator, and flaps are controled by hydraulic servos because hydraulics have advantages precision and powerloss, but on landing gear doors are controled by pnuematics(not servos)because you don't need any position feedback you only want to know doors are open or not.

You bring up some good points, it would be helpful to include some additional explanations of the advantages and disadvantages you mention.

Yeah, precision would be the deal breaker.  This is why excavators, for instance, use hydraulics because you can deliver a lot of power with very minute movements.  Good operators could pick up a quarter then knock over a tree.  So while in flight, control surfaces are subject to enormous pounds of air pressure but must move only a few inches and with a within a rapid response time.  A liquid is going to have the viscosity for more "fluid" movements which is more susceptible to instantaneous responses.  You'll see pneumatic systems a lot in plants for valve applications which will be fully open or fully closed.  Because air is so light is just can't deliver the same power and precision.
Besides fly by wire makes any of this talk rather obsolete.  You can get all the electrical power you need to extremely high HP/torque actuators that will deliver just as much force with even more precision and greater response time.
I'm not sure but I wouldn't doubt the wheel braking system might be pneumatic like over-the-road 18 wheelers.  Otherwise the only pressurized air you're ever going to see on a airliner will be cabin pressure and oxygen delivery.

Viscosity has nothing to do with this. Liquid is going to have higher viscosity, which means more power will be lost to internal friction as the fluid flows through the pipes. The reason for using liquids is their incompressibility, which allows them to transfer large forces (pressure) with minuscule changes in position.

Fly-by-wire doesn't (currently) uses electrical actuators, but still hydraulics, or a mix of hydraulics and electrical for redundancy. When the system falls back on electrical, the control may be limited or slow.

Fly by wire aircraft still use hydraulics for most of their actuators, because electric motors can have high torque or high precision, but they don't have both.

@JanHudec Why not?

@JanHudec The thing is, if looking at energy consumption, a hydraulic motion system for a simulator always consumes maximum power, whether the payload is moving or not. The excess energy not used for motion is transformed into heat at the servo valves. An electric motion system only consumes the energy directly used for motion (or compensating for gravity if no air spring is present). The force feedback systems at Level D flight controls have been electric torque motors as well for the last 20 years: silent, clean, frugal with energy. Granted the motors are bigger than hydraulic actuators.

@Koyovis, hm, strange. I can see reason why electric actuator would need constant power (unless holding force is provided by friction in a jackscrew, the electromagnets need power to maintain force—and jackscrews are slow), I don't see a reason for hydraulic actuator to need it (in steady state the fluid shouldn't be moving, so it shouldn't be losing pressure and therefore shouldn't need replenishing it; in fact, brakes do work from backup pressure reservoir for limited number of applications, but unlimited time, suggesting they indeed don't lose energy in steady state).


text:
What's a "gateway operation"?
From an AvWeb post regarding Trump's upcoming vacation to Florida:

Anyone planning to fly in the area should be aware of the potential
  for Notams that might include gateway operations.

What's a "gateway operation"?

Looking at this FAA notice from the 2012 RNC convention in Florida, there are multiple references to "gateway operations" and "gateway airport(s)". Specifically:

Aircraft not operating under a TSA-approved standard security program ... when the TFR is in effect must be security screened by TSA at a designated gateway airport or location.
  ...
  TSA security screening and gateway operations will be available on August 26 for those operators wishing to operate into St. Petersburg-Clearwater International Airport.
  ...
  TSA security screening at the gateway locations will consist of ID
  verification of all passengers and crew, watchlist matching, physical screening of persons and baggage, and inspection of the aircraft.
  ...
  Positive pilot identification procedures will be in effect during this TFR. Special ATC procedures and routes to and from this airport may be assigned prior to departure from a gateway airport. Upon departing the gateway airport, all aircraft must be on a VFR or IFR flight plan, maintain radio contact with ATC and continuously squawk an ATC-assigned discrete transponder code. Intermediate stops are not authorized unless there is an emergency. If an intermediate stop occurs, aircraft will be required to return to a gateway airport to be re-screened prior to continuing flight with the TFR

Then referencing this TSA post:

Dulles International Airport (IAD) will serve as the newest gateway airport, allowing certain pre-cleared general aviation operations, including corporate aircraft, charter flights, and on-demand operations, to fly directly into Ronald Reagan Washington National Airport (DCA).
  ...
  Aircraft must arrive from one of 17 gateway airports after flight crews have been vetted and passengers screened.

So it would appear that "Gateway operations" are specific security protocols for departing and arriving aircraft within a certain restricted area.
EDIT:
It appears that, if "Gateway Airports" and "Gateway Operations" are synonymous, that it is about strict preclearance procedures defined post 9/11. As far as I can tell, these restrictions are permanently in place for flights in Ronald Reagan National Airport (DCA), due to the obvious risk the airport's proximity poses to various Federal government buildings.
These rules are called "DASSP" for DCA Access Standard Security Program. The consist of the following regulations

TSA inspection of crew and passengers.
      TSA inspection of property (accessible and checked) and aircraft.
      The start and end dates of flight must be indicated on the TSA flight authorization.
      Identification checks of passengers by TSA.
      Submission of passenger and crew manifests 24 hours in advance of flight.
      Enhanced background checks for all passengers and fingerprint based criminal history records check (CHRC) for flight crew.
      Armed Security Officer (ASO) on board each flight.
      All operations are subject to cancellation at any time.
      All unscheduled operations to/from DCA require an FAA Slot Reservation.


text:
How much more economical are planes with retractable gears vs. those with fixed gears?
Many small planes have fixed gears, some have retractable gears. All things being equal, the plane with retractable gears would have to be more expensive than fixed gears, as the mechanisms involved in retracting them is obviously more complicated than fixed gears. On the other hand, planes with fixed gears should have somewhat more drag than a similar plane with retractable gears when they're retracted. This would imply that a plane with retractable gears would consume less fuel than one with fixed gears. If the difference could be quantified, how much more economical would the plane with retractable gears be vs. one with fixed gears?

I guess you meant to write "planes with fixed gears should have somewhat more drag than a similar plane with retractable gears"

The difference is quantifiable. Look at the difference between the Cardinal 177's with fixed gear vs the retractable ones. Or the 172 RG's vs conventional.

It is pretty common for retractable gear to allow an aircraft to fly faster, on the same engine, instead of to fly at the same speed, with lower fuel burn (although there is always a choice of what throttle setting to use)  Additionally, realize that retractable gear generally adds weight to an aircraft as well, which further complicates things.

Cardinal's with fixed gear (FG) can supposedly be almost as fast as retractable  gear (RG) when equipped with good aerodynamic fairings.  I'm changing mine now - better nose wheel pant with fairing to clean up the nosewheel scissor; better  main gear wheel pants with a more aerodynamic fairing over the leg and the top and bottom of the leg fairing; a better tailcone fairing to close gaps around the stabilator trim tab rod; and a fairing around the exhaust pipe.  Once the paper all settles, we'll see how it does!  RGs also have 20HP more to haul their extra gear retraction stuff.

@PeterKämpf, yes, that is what I meant to type. Unfortunately, fingers and brain couldn't get it together, and I didn't catch it before submitting. Thanks to fooot for correcting that.

Consider the Piper Turbo Arrow IV vs. the Piper Turbo Dakota... Same max gross weight, same engine, same wing, but the Arrow (with retractable gear) is nearly 12% faster at full cruise power.  This would imply that, at the Dakota's cruise speed, the Arrow should burn roughly 14% less fuel (give or take a little; it's 75% vs. 65% power, but at different altitudes).  Given this, the Arrow will cost less to fly for a given trip ($/nm).  The trade-off is that the Arrow costs more to buy, maintain, and insure, while having a smaller useful load.
Note that I chose these models for a reason: The Turbo Dakota is literally a fixed-gear version of the Turbo Arrow IV with no other major changes.  In most cases where a model is available in both fixed and retract, the retract has a more powerful engine.  This makes comparisons much more difficult.  YMMV

Fuel costs are one thing, don’t forget maintenance costs as well.

@RoboKaren lemme just edit to make that clear...  Thanks!

Just to make sure I'm covering everything, I'm only counting fuel, oil, TBO items, and a minor set-aside in the cost per mile.  The remaining costs (insurance, parking, annual, repairs, etc.) are important, but without knowing how many hours / miles to spread them over, I don't really include them in the hourly/per mile costs.  The Arrow is still cheaper per mile (because it is enough faster), but probably will cost more overall.

One thing to consider is your drag profile and mission requirements. If you have a cumbersome aircraft with high amounts of drag cruising at slower speeds vs. an aircraft designed for impressive maneuverability and high speed, the impact of adding a fixed gear becomes much more drastic. For the cumbersome craft, going with a fixed gear might be much more economical because the complexity and cost is so much less and the added drag of having a fixed gear might not noticeably affect the design parameters. For the other example, the added drag of having a fixed gear would substantially diminish the craft's capabilities. I don't think you can simply put a standard "quantification" to the economical benefit because in the end, the benefit/detriment of having a fixed gear vs. retractable gear really depends on the aircraft.

And don't forget, there's two types of RG pilots - those who have, and those who will.      (land gear up, that is - and not always of their own making).    If you really want to move fast, put on a turbo, or turbonormalizer, to maintain sealevel engine HP up into the lower drag atmosphere, up where O2 is needed.  I'm good with less maintenance, lower insurance, and hopefully speed increase with faster fairing.  Have only been to 12,500 ft once, to cross the Rockies leaving the Mount Rushmore area heading southwest. 10,500 ft is normally enough for east coast and mid-continent flying.


text:
Can the new multi scan weather radar on the A320 see low level cumulus?
Is it true that in the new multi scan weather radars fitted in the A320, low level cumulus clouds are not picked up?

HI Welcome to Stack Exchange Aviation.  Please post a citation for your assertion.  Without some sort of reference, how can it be possible to answer your question?

I'm not sure where you got your info from, but here is what I know of the Multiscan radars from Collins and Honeywell:
Multiscan displays precipitation from the highest tilt to the lowest so if the cloud is dense enough, even if it's a low level cloud, it will still cause returns. Keep in mind - just because the clouds are cumulus doesn't mean it has enough density to cause the WX-Radar to display any returns.
If you're talking about the dark-cockpit-concept, then yes, at certain high altitudes, the clouds will not show on the radar. This is because the OEMs want us pilots to only see what will pose a potential risk of turbulence and safety while at that particular altitude. If you want to see what's directly underneath your aircraft, the radar should be set to manual mode. However, this only happens during cruising at high altitudes.


text:
Where can I find the number of commercial jets that a country or airline purchases annually?
Is there any authoritative source from where we can find out the number of commercial jets that a country or airline purchases annually?

Do you want to count options as well?

Wikipedia mentions is for many airlines and for manufacturers too.

@ Burhan Khalid - I can take the option factor into account as well.  @ Farhan - Wikipedia does not mention for every airline

planespotters.net lists, for many commercial airlines, all their airplanes along with their delivery dates.
As for an authoritative source, you would have to look at the IATA or any other paying site such as airfleets.net.

Wikipedia lists are nice, but think about this question backwards to get the authoritative source. Find and parse the manufacturer data on the exact number of airliners sold.
Examples:

Airbus (or direct link to the spreadsheet download on that page)
Boeing (lots of nice filtering options!)

You could search for older reports or archives of previous years.


text:
Acceleration of a supersonic aircraft after breaking the sound barrier
People on the physics stackexchange recommended I ask here, so I am pasting my question regarding supersonic aircraft.
I stumbled upon an interesting plot; in particular, the dependence of wave drag on the Mach number:

It is curious to see that the drag coefficient drops so abruptly in the supersonic regime, but I am even more curious if the total drag force acting on the airplane also drops, i.e. if the plane starts accelerating in the supersonic regime.
I did some quick analysis of the problem. The drag force is defined as
$$F_{\text{drag}} = C(v) v^2 ,$$
where $C(v) = A C_D(v) \rho(v)/2$ is the newly introduced drag constant with the drag coefficient $C_D(v)$, flight medium density $\rho(v)$, and cross-sectional area $A$.
Assuming these relations, one can taylor expand the equation for the drag force to find that
$$\Delta F_{\text{drag}} = C'(v)v^2 \Delta v + 2Cv \Delta v.$$
As $C'(v)$ is clearly negative in the supersonic regime, this means that the total drag force drops if
$$C'(v) < -\frac{2C(v)}{v}.$$
It seems that this criterion could indeed be satisfied in air, as the right hand term in the inequality is a fairly small number.
Is there anyone that could elaborate further on what actually happens to the drag force as the plane breaks the sound barrier? Do the plane engines lower their power in order to maintain reasonable supersonic cruising speed, and if they didn't, would they be under too much heat load?

Your Taylor expansion only uses the first two terms, so it is only a crude approximation. But still, your observation is correct, however, whether it applies depends on the aerodynamic quality of the particular aircraft.
Practical supersonic aircraft have been designed to minimize the Mach drag peak. The ways to do this should be familiar:

Stretch the aircraft lengthwise so it becomes long and thin.
Smooth out the cross sectional area distribution over length ("area ruling")
Use swept wings with thin airfoils

If this is properly done, the drag peak will be small enough to have overall drag increase with Mach number above Mach 1. In case of the F-16 the drag coefficient rises from 0.02 (subsonic) to 0.045 (Mach 1.1) and stays roughly constant with increasing Mach number, so the absolute drag still grows with speed squared. No significant decrease in the drag coefficient occurs because of the complex flow
around the entire aircraft. Only when you have a poor design will drag actually become lower at low supersonic Mach numbers.
Another factor is thrust: Since ram pressure at the intake increases, so does thrust of the same engine as speed increases. This is the main reason why Concorde could already super-cruise 20 years prior to Lockheed marketing inventing this term.

Thank you Peter! Are you aware of any instance when an aircraft was designed badly enough to make this effect actually manifest?

@Akerai: I have no numbers but am sure that many of the early designs which transversed the Mach barrier by brute force are good candidates for a search.

most excellent exposition!

Here's another drag coefficient graphic with more information:

This is noticeable in practice: Concorde used its afterburners to accelerate from Mach 0.9 to 1.7 (while climbing), and then shut down the afterburners for its Mach 2 cruise flight.
Whether the total drag force drops, I don't know. But the difference in Cd is a factor of 3, while total drag has a v2 term, which would mean a 4x increase going from Mach 1 to M2, so total drag still increases.

In the wikipedia of the plot you've shown it states that it is a "Qualitative variation in Cd factor with Mach number for aircraft", so I am not sure if you should depend on the numbers shown.
At the same time, I understand that even if the force was to drop, it would eventually rise again due to the quadratic speed term. I am just curious if the slope of the drag coefficient is sufficiently negative to outdo the quadratic increase, at least just after reaching the maximum.

@Akerai this phenomena seems to be similar to the reduction in drag when the stern of a boat breaks free from its wake.  There is a reduction in overall drag and increase in speed.  However airflow cooling if the engines may not be a serious issue.  Increased speed and better ram efficiency approaching Mach 2 would help cancel increased overall drag.  Concorde would like to go faster and higher, but frictional heating of leading edges limit it to Mach 2 at around 60,000 feet.  Fuel consumption per mile for a given weight will tell the true story.